Question

Increasing the liquor level in the evaporator results in the

• A. Increased steam economy
• B. Decreased steam economy
• C. Increased steam capacity
• D. Decreased steam capacity

Hint:

Higher liquor level increases hydrostatic head and reduces effective temperature difference, so evaporator capacity decreases.

Answer 1

The Correct Option is D

In an evaporator, liquor level affects boiling and heat transfer. If the liquor level is increased too much, the hydrostatic head of liquid increases. Due to this, the boiling point of liquid at the heating surface increases. This reduces the effective temperature difference between steam and boiling liquid. Heat transfer rate depends on: \[ Q=UA\Delta T \] If effective temperature difference decreases, the evaporation rate decreases. The capacity of evaporator means the amount of water evaporated per unit time. When evaporation rate decreases, steam capacity also decreases. Therefore, increasing the liquor level in the evaporator results in: \[ \text{decreased steam capacity} \]